The Tagus is the longest river in the Iberian Peninsula, flowing approximately 1,007 kilometers (625 miles) from its source in Spain to its mouth at the Atlantic Ocean near Lisbon, Portugal. It passes through several cities, including Toledo and Almada, and is an important waterway for both countries. The river has played a significant role in history, serving as a natural boundary and a vital resource for agriculture and transportation. Its basin supports diverse ecosystems and is home to various species of fish and birds, making it an essential area for biodiversity in the region.